The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This invention relates generally to the field of treating a subterranean formation to increase the production of hydrocarbon from a formation. More specifically, the invention provides a method using a treatment fluid and diversion agent.
Hydraulic fracturing involves injecting fluids into a subterranean formation at pressures sufficient to form fractures in the formation, and the resulting fractures increase flow of production fluids from the formation to the wellbore. In chemical stimulation, flow capacity is improved by using chemicals to alter formation properties, such as increasing effective permeability by dissolving materials in or etching the subterranean formation. A wellbore may be an open hole or a cased hole where a metal pipe called a casing is placed into the drilled hole and often cemented in place or isolated with devices that expand to seal between the casing and wellbore. In a cased wellbore, the casing is perforated in specified locations to allow hydrocarbon flow into the wellbore or to permit treatment fluids to flow from the wellbore to the formation.
To access hydrocarbon effectively and efficiently, it is desirable to direct the treatment fluid to target zones of interest in a subterranean formation. There may be target zones of interest within various subterranean formations or multiple layers within a particular formation that are preferred for treatment. In such situations, it is preferred to treat the target zones or multiple layers without inefficiently treating zones or layers that are not of interest, e.g. nonproducing zones or zones with high water and/or gas content. In general, treatment fluid flows along the path of least resistance. For example, in a large formation having multiple zones, a treatment fluid would tend to dissipate in the portions of the formation that have the lowest pressure gradient or portions of the formation that require the least force to initiate a fracture. Similarly in horizontal wells, and particularly horizontal wells having long laterals, the treatment fluid dissipates in the portions of the formation requiring lower forces to initiate a fracture, often near the heel of the lateral section, and less treatment fluid is provided to other portions of the lateral. Once treatment of a zone or formation is completed it is desirable to treat another zone. Also, it is desirable to avoid stimulating undesirable zones, such as water-bearing or non -hydrocarbon bearing zones. Thus it is helpful to use methods to divert the treatment fluid to target zones of interest or away from undesirable zones.
Diversion methods are known to facilitate treatment of a specific interval or intervals. Ball sealers are mechanical devices that frequently are used to seal perforations in some zones thereby diverting treatment fluids to other perforations. In theory, use of ball sealers to seal perforations permits treatment to proceed zone by zone depending on relative breakdown pressures or permeability. But frequently ball sealers prematurely seat on one or more of the open perforations, resulting in two or more zones being treated simultaneously. Likewise, when perforated zones are in close proximity, ball sealers have been found to be ineffective. In addition, ball sealers are useful only when the casing is cemented in place. Without cement between the casing and the borehole wall, the treatment fluid can flow through a perforation without a ball sealer and travel in the annulus behind the casing to any formation. Ball sealers have limited use in horizontal wells owing to the effects of formation pressure, pump pressure, and gravity in horizontal sections, as well as the possibility that laterals in horizontal wells may not be cemented in place.
Other mechanical devices used for diversion include bridge plugs, packers, down-hole valves, sliding sleeves, and baffle/plug combinations; and particulate placement. As a group, use of such mechanical devices for diversion tends to be time consuming and expensive, making them operationally unattractive, particularly in situations where there are many target zones of interest.
Chemically formulated fluid systems are known for use in diversion methods and include viscous fluids, gels, foams, or other fluids. Many of the known chemically formulated diversion agents are permanent (not reversible) in nature and some may damage the formation. In addition, some chemical methods may lack the physical structure and durability to effectively divert fluids pumped at high pressure or they may undesirably affect formation properties. The term diversion agent herein refers to mechanical devices, chemical fluid systems, combinations thereof, and methods of use for blocking flow into or out of a particular zone or a given set of
Degradable materials have been used for fluid loss control. Examples include rock salt, graded rock salt, benzoic acid flakes, wax beads, wax buttons, oil-soluble resin material, etc. Degradable materials have also been used to facilitate proppant transport, such as disclosed in U.S. Pat. No. 7,275,596. Commonly assigned U.S. Pat. No. 7,565,929 discloses degradable material assisted diversion methods and compositions.
A method of reliably treating target zones in a subterranean formation using a diversion agent without plugging or bridging the next zone or formation in the treating sequence would be desirable. A method in which producing zones in the same well bore could be treated serially using the same downhole equipment without intervening wireline operations would also be desirable. Ideally, such methods might facilitate an upper-to-lower zone treatment protocol or mixture of order based on best completion options in the appropriate circumstances, rather than the prevailing lower-to-upper protocol currently in use.